How do I do addition on only the first two columns of an array?

I have an array (attached: motion) that is a 2 x 1 x 20 double. I want to subtract [20 20] from the first two columns, but preserve the third. So for example, for one row:

motion =  [18 20 1]
marker = [20 20]
result of motion - marker = [-2 0 1]

row two would look like:

motion = [19 21 2]
marker = [20 20]
result of motion - marker = [-1 1 2]

I am sure this is simple but I am making it more difficult than it needs to be I think. Thanks!

Answer 1

[the cyclist]

I'm pretty confused by your question, and in particular how you are referring to your "columns" and "rows". I downloaded your MAT file. The array Trans has 2 rows (the 1st dimension), 1 column (the 2nd dimension), and "depth" of 20 (the third dimension).

Trans(:,:,1) is

 [20;
  20]

and Trans(:,:,20) is

[21;
 19]

Are you saying that you want those to become

[0;
 0]

and

[ 1;
 -1]

respectively?

If so, that is very simple.

out = Trans - 20;

If that is not what you mean, please give some more detail about what you want for output.

[geog170]

Thank you for weeding through my request, I just started using matlab regularly. This is exactly what I needed:

out = Trans - 20;